This is, of course, a matter of opinion. It is from the realm of "normative" as opposed to "positive" economics.
On the one hand, national income per capita gives us a good idea about how much money is available to people in a given country. It makes sense, for example, to say that Americans are better off than Chinese because America's national income per capita is so much higher than China's. We know that Americans can afford many more goods and services than Chinese can.
But is money the only thing that matters? Take, for instance, European countries that have less income but where people are given more vacation days. Who is better off -- those who make more money, or those who have more leisure?
On a more national note, compare a country that is somewhat poorer, but has a more equal income distribution, with one that is richer but more stratified. Which country is better off?
In both cases, these are matters for opinion and no one's answer is better than anyone else's.